More or less. KC mentioned Nighthawk, but there's also Radisphere and one or two others that I'm blanking on. They will hire on rads for a reduced salary compared to what they may make in a standard PP group.
There are even reports that since rads have been farming out their night reads to these companies, they've become more powerful and predatory and have swooped in, undercut the prior rad group and taken their hospital contract.
In addition, there're also self-referral issues with ortho groups and neuro groups buying their own MRIs in order to collect the TC. Not sure if those guys have started demanding a share of the PC as well though.
All this info has been from AuntMinnie.com, the major radiology forum. You do need to sign up and become a member to read the forums though (but it's free).